When swapping a 4L80E into a 2WD extended cab truck, what yoke/flexplate/converter details need sorting for the driveshaft and converter to fit?

Flexplate/converter: the 4L80E converter uses the 11.5 in bolt pattern, so you need a 4L80E-pattern flexplate (a 4L60E flexplate is 11.062 in). On an LS that came with a 4L80E, the factory flexplate works.

Yoke: the 4L80E takes the GM 32-spline yoke (the same family as a TH400 without the threaded output shaft).

Driveshaft length: the 4L80E is longer than a 4L60E, so re-measure:

How to measure (Speedway's method):

1. Put the rear axle at ride height — not hanging with the car in the air.
2. Measure from the flat face of the rear yoke (the center of the U-joint once installed)…
3. …to the seal surface on the back of the transmission tailshaft housing — not to the end of the output shaft, which makes the number come out short.
4. That one number, plus the correct front yoke and U-joints, is what a custom driveshaft is built to.

Speedway's custom-length kits are rated up to 400 hp (small kit), 600 hp (3 in steel kits) and 1,200 hp (chromoly).